Ultrastructural appearance of chondroblastoma

International

International Orthopaedics (SICOT) (1994) 18:389-392

Orthopaedics © Springer-Verlag 1994

Ultrastructural appearance of chondroblastoma M. Fadda, A. Manunta, G. Rinonapoli, G. Zirattu, and E. De Santis Orthopaedic Department, University of Sassari, c.p. 40, 1-07100 Sassari, Italy Accepted: 2 May 1994

Summary. The ultrastructural appearance of two chondroblastoma were examined by scanning and transmission electron microscopy. The polygonal basal cells, with a scanty pericellular matrix, show a poorly developed endoplasmic reticulum and many Golgi bodies. The highly differentiated chondroid cells are assembled in isogenous clusters and show intracytoplasmic inclusions of glycogen and lipids, numerous mitochondria and superficial secretion vesicles arising from a well developed rough endoplasmic reticulum. Clusters of crystals, in close contact with the matrix collagen fibres, are found near to the tumour cells. These ultrastructural characteristics, together with the basal undifferentiated cells that plvliferate and differentiate into cartilaginous tissue, distinguish this neoplasm from chondroma, mesenchymal chondrosarcoma and chondromyxoid fibroma and confirm its chondroid origin. R~sum~. Les auteurs ont compare les aspects ultrastructuraux de deux chondroblastomes, au microscope Electronique ~ balayage et au microscope dlectronique ~ transmission, afin d'Evaluer l'histogEnkse de la lesion. Les cellules basales, polyEdriques et amassEes, avec une matrice pEricellulaire peu abondante, prEsentent un rEticulum endoplasmique peu dEveloppE et des systbmes de Golgi souvent dilates et multiples. Les cellules qui prEsentent la diffErenciation chondrofde la plus marquee sont rEunies dans des groupes isogbnes, montrant des inclusions de glycog~ne et de lipides dans le cytoplasme, de nombreuses mitochondries renflEes et, en surface, des vEsicules de sEcrEtion Reprint requests to: M. Fadda

provenant d'un rEticulum endoplasmique bien dEveloppE. On observe, tout prks de la cellule tumorale, des bouquets de cristaux en contact direct avec les fibres collagbnes de la matrice. La presence de cellules basales indiffErenciEes qui prolifOrent et se diffErencient en tissu cartilagineux distingue cette nEoplasie des autres (chondrome, chondrosarcome mEsenchymal et fibrome chondromyxo~de) et permet de Ia classer parmi les lesions d'origine chondroMe.

Introduction Chondroblastoma is a rare benign tumour of bone accounting for 1% of all skeletal tumours [3]. It is usually located in the epiphyseal regions, and does not have well defined clinical, radiological and histological features [4, 13]. Some studies have used light and electron microscopy, and have distinguished two cellular components, namely, cells with chondroid differentiation and polymorphous basal cells. The mosaic arrangement of the chondroblastic cells supports the view that the neoplasm originates in cartilaginous cells [2, 8, 9]. This is confirmed by immuno-histochemical studies demonstrating the presence of S-100 protein in chondroblastoma, which is also found in human chondrocytes [1, 11, 15]. Others have maintained that the tumour cells arise from histiocytes because of the argyrophilic reticulum around them and the study of in vivo cultures of neoplastic basal cells [7, 14]. Recently, it has been suggested that the chondroblastoma originates from a mix of chon-

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M. Fadda et al.: Ultrastructural appearances of chondroblastoma

Fig. 1. a Radiograph showing a chondroblastoma in the proximal femoral epiphysis which was treated by curettage and bone grafting, b Light microscopy of this tumour shows basal mononucleate polygonal cells (on the left) which differentiate towards chondrocytic elements with calcification and necrosis

(seen on the right). HE x94. c Radiograph of a chondroblastoma of the proximal tibial epiphysis (arrows)which involves the subchondral bone plate; the histological appearance is the same as in b

drocytic and histiocytic tumour cells, and not f r o m articular or epiphyseal cartilage [12]. Attempts have been made to solve the problem by carrying out ultrastructural studies using transmission electron microscopy (TEM) on well defined cellular areas of the chondroblastic lesion [5, 7, 10, 12]. No reports of scanning electron microscopic (SEM) studies have been found. In the present study, we analyse the ultrastructural changes in two chondroblastoma seen in our department using both T E M and SEM.

Results

Materials and methods Two patients underwent curettage and autogenous bone grafting as treatment for ehondroblastoma. One was a woman, aged 18 years, whose tumour was in the proximal epiphysis of the femur, the other was a man, aged 21 years, with a turnout in the proximal epiphysis of the tibia. The radiological and histological appearances were typical of the tumour (Fig. 1). Specimens were taken from selected areas and prepared by the usual methods for SEM and TEM. The largest fragments of tissue were fixed in 2.5% glutaraldehyde buffered with pH 7.5 phosphate, post-fixed in 1% osmium, dried in CO2, metallised in colloidal gold in a vacuum evaporator, and were examined under an ISI DS scanning electron microscope operating at 20 Kv. The other part was subdivided into smaller fragments and then sectioned into 1 mm cubes. These were fixed in 2.5% glutaraldehyde and PBS, post-fixed in osmium tetroxide and embedded in araldite. Examination of the semi-thin sections, after they had been stained with toluidine blue, allowed selection of the most typical areas of the neoplasm and provided ultra-thin sections that were stained with uranyl acetate and lead citrate, and examined using a Zeiss EM 109 transmission microscope.

Scanning electron microscopy The most immature tissue which had the highest cellular density was made up o f clusters o f polymorphous cells, tightly packed together, corresponding to the basal cells (Fig. 2). The tissue with the highest chondroid differentiation takes up the widest area of the lesion and was more easily observed by SEM. Chondrocytic lacunae, isolated or gathered in isogenous clusters, showed calcified globular formations, closely connected with the surrounding collagen fibres where they were close to the edge of the lacunae (Fig. 3). The arrangement o f the collagen fibres was not homogenous. The fibrillary network was more dense near the edge o f the chondrocytes, but appeared to be more rarefied in the farther part of the cellular m e m brane (Fig. 4).

Transmission electron microscopy The basal cells were found in the most immature areas of the tumour. T h e y were very close together and had very wide nuclei. Numerous microvilli projected from the cellular membrane. The endoplasmic reticulum in the cytoplasm was poorly developed, the Golgi bodies were often expanded and multiple, and there were a small n u m b e r of organelles (Fig. 5). Transitional forms could be detected between the basal polygonal cells. Their nucleus-cytoplasm ratio was negative, but folding of the cellular m e m b r a n e could be seen together with a swollen rough endoplasmic reticulum with secretion vesicles which were full of isolated

M. Fadda et al.: Ultrastructural appearances of chondroblastoma

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Fig. 2 SEM of the most chondroid differentiated area: the polymorphous basal cells are organised in clusters of many ceils. ×2695

Fig. 5. TEM of the immature basal cells which are packed close together; the nucleus-cytoplasm ratio is negative; the organelle mostly frequently seen is the Golgi apparatus, x4950

Fig. 3 a, b. SEM of the most differentiated area. a Areas of calcification are seen close to a chondrocytic lacunar depression. x 1997. b Detail of the calcified globules with fundamental substance, x3560

Fig. 6 a-e. TEM of the most chondroid differentiated area.

Fig. 4. SEM of the most chondroid differentiated area showing the arrangement of the fibrous material of the matrix which coats and surrounds the cartilaginous cells, x 1458

show swollen mitochondria. ×2750. b A rough hyperplastic reticulum a r r o w s characterises the chondroid cells. × 12000. c Crystal filaments a r r o w s connected with the collagen are seen in the matrix. × 16500 a Arrows

392 electron-dense material. T h e r e were m a n y int r a c y t o p l a s m i c inclusions, g l y c o g e n granules and lipids were seen together with m a n y swollen mitochondria. G r o u p s of crystal filaments, which were closely connected to the collagen fibrils, w e r e seen near the t u m o u r cells (Fig. 6).

Discussion The undifferentiated basal cells of a chondrob l a s t o m a undergo a rapid process o f multiplication and tend to differentiate through different stages into cells with the characteristics of cartilage. The t u m o u r cells situated in areas w h e r e the greatest chondroid differentiation is present are similar to the c h o n d r o c y t e s of normal epiphyseal cartilage. Nevertheless, the chondroid lacunae do not ever show a clear structural differentiation under SEM. T E M shows that the cells present a higher n u c l e u s - c y t o p l a s m ratio and a high int r a c y t o p l a s m i c content of g l y c o g e n and lipids [5, 12]. This helps to distinguish c h o n d r o b l a s t o m a , not only f r o m the cells o f n o r m a l epiphyseal cartilage, but f r o m other tumours such as m e s e n c h y m a l c h o n d r o s a r c o m a , c h o n d r o m y x o i d f i b r o m a and c h o n d r o m a which are m o r e differentiated [6, 15]. We found calcified globules in close contact with the pericellular collagen fibrils in the intercellular matrix. T h e s e represent the c o n s e q u e n c e o f a diminished circulation leading to death o f the n e w l y f o r m e d tissue. T h e s e findings all support the theory of the chondroid origin of c h o n d r o b l a s t o m a .

M. Fadda et al.: Ultrastructural appearances of chondroblastoma

References 1. Ascoli V, Facciolo E Muda AO, Martelli M, Nardi F (1992) Chondroblastoma of the rib presenting as an intrathoracic mass. Report of a case with fine needle aspiration biopsy, immunocytochemistry and electron microscopy. Acta Cytologica 36:423-429 2. Campanacci M, Giunti A, Martucci E, Trentani C (1977) Epiphyseal chondroblastoma: a study of 39 cases. Ital Orthop Traumatol 3:67-74 3. Dahlin DC, Ivins JC (1972) Benign chondroblastoma: a study of 125 cases. Cancer 30:401-413 4. De Santis E (1978) Considerazioni sul condroblastoma epifisario. Arch Putti 29: 85-110 5. De Santis E, Turbacci E Strazzullo E, Piantelli M (1980) Aspetti ultrastrutturali del condroblastoma dello scheletro. Arch Putti 30:79-88 6. Erlandson RA, Huvos AG (1974) Chondrosarcoma: a light and electron microscopy study. Cancer 34: 1642-1652 7. Higaki S, Takeyama S, Tateishi A, Machinami R, Abe M (1981) Clinicopathological study of twenty-two cases of benign chon&'oblastoma. J Japan Orthop Assoc 55: 647 - 664 8. Huvos AG, Marcove RC, Erlandson RD et al (1972) Chondroblastoma of bone: a clinico-pathologic and electron microscopy study. Cancer 29:760-771 9. Jaffe HL, Lichtenstein L (1942) Benign chondroblastoma of bone: reinterpretation of the so-called calcifying or chondromatous giant cell tumor. Am J Path 18:969-991 10. Levine GD, Bensch KG (1972) Chondroblastoma. The nature of the basic cell: a study by means of histochemistry, tissue culture, electron microscopy and autoradiography. Cancer 29: 1546-1562 11. Liu ZJ (1990) Histogenesis of chondroblastoma: a study of tissue culture, immunohistochemistry and electron microscopy. Chung-Hua Chung Liu Tsa Chih. 12:351-353 12. Morimoto K, Okada S (1992) Electron microscopic and immunohistochemical studies on chondroblastoma. J Japan Orthop Assoc 66:668-674 13. Pflueger P, Heinrich SD, Cravell R (1993) Chondroblastoma. Orthopedics 16:339-342 14. Schajowicz F, Gallardo H (1970) Epiphyseal chondroblastoma of bone. J Bone Joint Surg [Br] 52:200-226 15. Ushigome S, Takakuwa T, Shinagawa T, Tagaki M, Kishimoto H, Mori N (1984) Ultrastructure of cartilagineous tumors and S-100 protein in the tumors with reference to the histogenesis of chondroblastoma, chondromyxoid fibroma and mesenchimal chondrosarcoma. Acta Path Jap 34: 1285-1300